MIDDLESEX County Average 2005 NATA Modeled Air Concentrations Compared to Health Benchmarks

Pollutant

Modeled
Air Concentration (ug/m3)

Health
Benchmark (ug/m3)

Risk
Ratio

%
Contribution from

Point Sources

Nonpoint
Sources

On-road
Mobile Sources

Nonroad
Mobile Sources

Background & Secondary

Acetaldehyde

2.0

0.45

4.5

<1%

4%

7%

3%

86%*

Acrolein

0.059

0.020

3

<1%

18%

17%

9%

56%*

Arsenic Compounds

0.00072

0.00023

3.1

2%

6%

5%

3%

84%

Benzene

1.4

0.13

11

1%

13%

31%

12%

43%

1,3-Butadiene

0.095

0.033

2.9

<1%

<1%

46%

18%

36%

Cadmium Compounds

0.000097

0.00024

0.4

10%

37%

0%

<1%

53%

Carbon Tetrachloride

0.61

0.067

9.1

0%

<1%

0%

0%

100%

Chloroform

0.13

0.043

3

1%

52%

0%

0%

47%

Chromium (hexavalent form)

0

0.000083

3.9

21%

7%

4%

<1%

68%

Cobalt Compounds

0.000045

0.00011

0.4

87%

13%

0%

0%

0%

1,4-Dichlorobenzene

0.10

0.091

1.1

1%

54%

0%

0%

45%

1,3-Dichloropropene

0.11

0.25

0.4

0%

100%

0%

0%

0%

Diesel Particulate Matter

1.2

0.0033

381

0%

0%

57%

43%

0%

Ethylbenzene

0.39

0.4

1

2%

34%

42%

22%

0%

Ethylene Oxide

0.0096

0.011

0.9

14%

6%

0%

0%

80%

Formaldehyde

2.2

0.077

29

<1%

3%

10%

5%

82%*

Methyl Chloride

1.2

0.56

2.2

<1%

<1%

0%

0%

100%

Naphthalene

0.14

0.029

4.8

3%

45%

27%

3%

22%

Nickel Compounds

0.0013

0.0021

0.6

31%

25%

2%

2%

40%

PAH/POM

0.012

0.0072**

1.7

<1%

81%

10%

9%

0%

Perchloroethylene

0.29

0.17

1.7

<1%

43%

0%

0%

57%

1,1,2-Trichloroethane

7.6E-6

0.063

1.0E-4

87%

13%

0%

0%

0%

Chemicals with risk ratios greater than or equal to 1 are
in bold.
Risk Ratios based on noncarcinogenic effects are in italics.
The symbol ug/m3 is micrograms per cubic meter,
the amount (in micrograms) of a chemical in a cubic
meter of air. This is also known as a concentration.
For diesel particulate matter, onroad and nonroad
concentrations include a model-estimated background
concentration. *Acetaldehyde, acrolein and formaldehyde concentration estimates include secondary formation, which is the process by which chemicals in the air are transformed into other chemicals.**PAH/POM is "polycyclic aromatic hydrocarbons/polycyclic organic matter." These define a broad class of compounds. The chemicals making up this class were broken up into 8 groups based on toxicity, and each group was assigned a cancer-weighted toxicity estimate. 0.0072 ug/m3 is the health benchmark average across the 8 groups.